I reckon this one I can contribute to.
First of all, glad you're reworking kits, 100% needed.
Not exactly agreeing with the kits being overpowered, rather they reward playtime, not many players get past level 10 in my experience and where you might see it as becoming overpowered is around 10-13+.
Here's why they are not overpowered:
If a player reaches levels like that, he surely already has access to all these items, naturally acquired and laying in storage. As for some of the rare items:
1)They are there to assist with acquiring them in situation of the ever-growing server and amount of players hunting for said, (potentially scarce) resources.
2)Additionally, there's obviously a cooldown on most kits (up to 30 days on some).
3) A lot of people at these levels forget to redeem kits completely (at least in my experience).
So, back to the point: It's great, please do rework kits, however imo the focus should be on adding new items, released after multiple new updates. In other words, adapting the kits to current gameplay. Ultimately, the cooldown for every kits can always be adjusted.
Perhaps a survey is due, for players to respond which items are least wanted/used in every kits and what items they'd rather see in said kit.
Best of luck!
UPD: One more thing, I think to get some active responses, or rather specific ones, you should construct the new potential kits with the ideas provided in this thread and then let players vote. I like mike's response, maybe do limit kits, make 1-10 a repeatable affair, those might contain said scarce items, in limited quantities, and then 11-20 a one-time redeemable thing. Or maybe 1-3 (essential items), and work from there.